Stavros Koulouridis

Polymer–Ceramic Composites for Microwave Applications: Fabrication and Performance Assessment

We present a novel technique to fabricate conformal and pliable substrates for microwave applications including systems-on-package. The produced materials are fabricated by combining ceramic powders with polymers to generate a high-contrast substrate that is concurrently pliable (bendable). Several such polymer-ceramic substrates are fabricated and used to examine the performance of a patch antenna and a coupled line filter. This paper presents the substrate mixing method while measurements are given to evaluate the loss performance of the substrates. Overall, the fabricated composites lead to flexible substrates with a permittivity of up to epsivr=20 and sufficiently low loss

Study of the coupling between human head and cellular phone helical antennas

The interaction between normal-mode helical antennas and human head models is analyzed, using both a novel accurate semi-analytical method and finite-difference time-domain (FDTD) simulations. The semi-analytical method is based on the combination of Greens functions theory with the method of moments (Green/MoM) and is able to model arbitrarily shaped wire antennas radiating in the close proximity of layered lossy dielectric spheres representing simplified models of the human head. The purpose of the development of the Green/MoM technique is to provide a reliable tool for preliminary (worst case) estimation of human head exposure to the field generated by different antenna configurations with emphasis on the helical antenna, representing the most diffused antenna type used in modern cellular handsets. Furthermore, the accurate semi-analytical character of the Green/MoM technique permits the accuracy assessment of purely numerical techniques, such as the FDTD, which is currently the most widely used computational method in mobile communication dosimetric problems, since it allows modeling of anatomically based head models. After appropriate benchmarking, FDTD simulations are used to study the interaction between a heterogeneous anatomically correct model of the human head exposed to a normal-mode helix monopole operating at 1710 MHz mounted on the top of a metal box representing a realistic mobile communication terminal. The study of both canonical and realistic exposure problems includes computations of specific absorption rates (SARs) inside the human head, total power absorbed by the head and assessment of antenna performance. Emphasis is placed on the comparative dosimetric assessment between adults and children head models.

Multiobjective Optimal Antenna Design Based on Volumetric Material Optimization

There is growing interest for small antennas that concurrently have higher functionality and operability. Multiobjective optimization is an important tool in the design of such antennas since conflicting goals such as higher gain, increased bandwidth, and size reduction must be addressed simultaneously. In this paper, we present a novel optimization algorithm which permits full volumetric antenna design by combining genetic algorithms with a fast hybrid finite element-boundary integral method. To our knowledge, this is the first time that a full three dimensional antenna design is pursued using concurrent shape, size, metallization as well as dielectric and magnetic material volume optimization. In comparison to previous optimization pursuits, our approach employs a wide-frequency sweep using a single geometry model, thus, enhancing speed, along with several discrete material choices for realizable optimized designs. The developed algorithm can be interpreted as a three dimensional Pareto optimization scheme and provides the designer with several choices among the best antennas, according to design goals and constraints. The final designs are associated with very thin (~0.01lambda) material substrates and yield as much as 15% bandwidth using a 0.1lambda--0.4lambda aperture subject to various gain and bandwidth requirements

A Novel Reflective Surface for an UHF Spiral Antenna

As is well known, metallic cavity backings reduce antenna gain particularly for broadband configurations at low frequencies. This letter presents a novel reflective surface consisting of a ferrite tile with variable conductive coating as a backing for a conformal UHF spiral antenna. The ferrite material is used in the outer region to preserve the free-space antenna gain at low frequencies. Toward the center, the backing tapers to a conductive coating making it suitable for high frequency operation. It is shown that this hybrid surface (ferrite to metallic) improves the antenna performance significantly at lower frequencies without compromising the high frequency gain.

A Novel 1.5

A new global positioning system (GPS) antenna is proposed to cover the three GPS bands (L1, L2, and L5, namely 1575, 1227, and 1176 MHz) with the L5 band to be added after 2006. The developed antenna size is only

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Quadruple Antenna for Tri-Band GPS Applications

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PARAMETRIC STUDY OF POWER ABSORPTION PATTERNS INDUCED IN ADULT AND CHILD HEAD MODELS BY SMALL HELICAL ANTENNAS

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Design of a Novel Miniaturized Implantable PIFA for Biomedical Telemetry

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